Effects Of Feeding Patterns In Summer On Yaks’ Growth Performance,Carcass Traits, Meat Quality And Rumen Bacteria Diversity

The present study was conducted to investigate the effects of different feeding regimes on yaks’ growth performance, slaughter traits, carcass characteristics, meat quality and rumen bacterial diversity through four trials. The purpose of this study is to providescientific basefor supportingyaks’ feedingpractice in the summer season on Tibet Plateau.Exp.l A study was conducted to investigate the effects of different feeding regimes on yak growth performance and rumen fermentation characteristics.A total of48healthy Sibu bull yaks with4-5years old were selected and divided into four groups. Four feeding regimes as treatments were:(1) yaks free grazed (G group) on the summer pasture,(2) yaks grazed on the summer pasture with supplemented of2.0kg/d of hunger-allayed feed (GS group),(3) yaks fed in the feedlot regime with hunger-allayed feed used as a sole feed (F group), and (4) yaks fed in the feedlot regime supplemented with2.0kg/d mixed concentrate diet (FS group). The results showed that average daily gain (ADG) for G, GS, F and FS were504.2,537.1,302.6and611.6g/d, respectively.The groups of G, GS, and FS had greater ADG than F (P<0.01), although there were no significant difference among G, GS and FS (P>0.05). After feeding trial finished, all animals were slaughtered and rumen contents were sampled. Rumen concentrations of total VFA, acetate, propionate and butyrate of FS were notably higher (P<0.01)than G, GS and F, respectively, although there was no remarkable difference (P>0.05) among G, GS and F. The contents of ammonia and total plasma protein for FS, GS and G were much higher than those of F. Grazing in the summer maybe would be a first choice as yaks’feeding regime for the nourished pastures on Tibet region. Feedlot feeding with mixed concentrate supplement could prominently improve yaks’ growth performance and consequently would be another choice for yaks’feeding regime in the summer.Exp.2A trial was conducted to study the effect of different feeding regimes on slaughter performance, carcass traits and meat qualityof yaks.The experimental treatments werethe same as Exp.1. The results showed that FS and GS groups had higher (P<0.05) both hot and cold carcass weight, and net meat weight than F, although the differences were not significant among G, GS and FS. Net meat rate and ratio of meat to bone were32.48and3.43%, respectively for F, which were significantly lower CP<0.05) than G, GS and FS, respectively. The ribeye areas of G, GS and FS were27.33,27.56and26.76cm2, respectively, which were much higher (P<0.05) than that of F (20.54cm2). There were no obvious differences (P>0.05) in pH value, shear force, cooking loss, drip loss, back fat thickness over LD, fat color, proportions of dry matter, moisture, ash and cholesterol among G, GS, F and FS, respectively.The CP content in G and GS were87.50and86.87%, respectively, which were remarkably higher (P<0.05) than that of F (82.67%) and FS (82.95%), respectively. The crude fat contents of G and GS were8.02and8.24%, respectively, which were notably lower (P<0.01) than that of F (11.08%) and FS (11.35%). In contrast, a-linolenic acid, ω-3UFA,Leu, Ile, Phe and Met amino acid content were remarkably higher (P<0.05) than those of F and FS, respectively. Myristic acid, palmitic acid and palmitoleic acid of F and FS were remarkably higher (P<0.05) than those of G and GS, respectively. Generally, F feeding regime showed the lowest slaughter trait, whereas FS feeding regime had the highest slaughter trait among the four treatments. Using the feeding regimes of G and GS, the contents of amino acids and fatty acidswere improved compared with the regimes of F and FS.Exp.3A study was conducted using PCR-DGGE technology to investigate the effects of different feeding regimes on the diversity of rumen bacteria. The experimental design was the same as Exp.l. The result showed that different feeding regimes displayed abundant bands in DGGE fingerprint, but there was no remarkable difference among4treatments through analysis of diversity indexes. According to clustering analysis, different individual was clustered together to form a small branch according to different feeding patterns (G, GS, F or FS treatments), then formed more bigger graze branch (including G and GS) and feedlot feeding branch (including F and FS). It seemed that different feeding regimes still affected the diversity of yaks’ rumen bacteria populations, but the difference was not significant in statistics.Exp.4A study was conducted to investigate the rumen bacterial classification and diversity of yaks (Bosgrunniens) fed by grazing or feedlot feeding regime on the Tibetan Plateau by analysis of16S rRNA gene libraries. A total of212clones (107clones from feedlot feeding regime,105clones from grazing) were obtained from two libraries (library A and library B), divided into162OTUs (86OTUs and89OTUs in library A and library B, respectively) in accordance with the criteria that sequence mutual similarity of97%or greater was defined as one operational taxonomic unit (OTU), therein, the two libraries shared13OTUs. It was found that13.8%of clones in library A and12.38%of clones in library B had a similarity of97%or more with the cultured species; the similarity of54.21%and60.95%of clones in library A and B, respectively with the known bacterium for all less than90%. Ruminococcus albus, Ruminococcus flavefaciens and Butyrivibrio fibrisolvens, as representatives of the known bacterium species, were all detected in library A and library B. Whereas Selenomonas ruminantium, Succiniclasticum ruminis, and Butyrivibrio proteoclasticus emerged only in library B, and Pseudobutyrivibrio ruminis and Roseburia faecis appeared only in library A. According to the phylogenetic analysis, a total of84.88%OTUs (91clones) in library A and73.03%OTUs (78clones) in library belong to LGCGPB (Low G+C Gram Positive Bacteria) subdivision. A total of15.21%OTU (16clones) in library A and24.72%OTU (25clones) belong to CFB (Cytophaga/Flexibacteria/Bacteroites) subdivision. Only two clones clustered with Proteobacteria in library B, and no clones collected with Archaea, Spirochaetes and HGCGPB (High G+CGram Positive Bacterial) subdivisions in phylogenetic trees from library A and B. In conclusion, HGCGPB subdivisions and CFB subdivisions were the mainly composition of yaks rumen bacterial. Indoor-feeding and grazing had an effect on rumen bacterial diversity in Yaks rumen.